Cabin pressure control instrument



Oct. 7, 1952 l B. E. DEI. MA'R CABIN PRESSURE CONTROL' INSTRMENT Filed Dec. 9, 1950 2 SHEETS-SHEET 1 LEV Oct. H7, 1952 B. E. DEL MAR CABIN PRESSURE CONTROL INSTRUMENT 2 SHEETS-SHEET 2 Filed Dec. 9. 1950 2 4 2 a /0 /2 /4 /2/2 202224 2525 2022# ,4a/radi -27/01/54//0/-25' .IN VEN TOR. 292062' 22 A442 Afrae/E/ Patented Oct. 7, 1,952

CABINVPBEssURE ooN'rRoL INs'iRUM'r Bruce E. Del Mar, Los Angeles, Calif., assigner 'to i v Douglas Aircraft Company, Inc.,V Santa Monica, j'

Calif.

Appueeuen Deeember 0, 1950, serial ne. 200,045

i', 1 This inventiony relates towpressure responsive 'instrumentsand more vparticularly to lsuch instruments especially useful in systems for controlling'pressure of the air of aircraft cabins. This application is a continuation-in-part of myv copending applications Serial No. 443,233, now Patentio. 2,549,672, and Serial'No.` 669,366, now PatentNo. 2,549,673, led May 16, 1942 and May 13,1946' respectively. In the pressure controlling systems thereinshown, as `inall such systems, theabsolute pressureiof cabin air is varied by controllably varying the rate of air dischargefromlthe cabin relative to the rate of the air delivery y to thecabin. The air ldelivered to the v(.Labnl is furnished by superchargers or like blowerswhichare capable of delivering air to the cabin atv pressures greater than 4flight or ambient'pressure. Such blowers will operate efflciently so long as the ratio of the outlet pressure toninletpressure does not exceed the design limit of the blower. This ratio iscommonly termed the compression ratio of the blower and is one which can be readily determined.

A s the aircraft ascends the ratio of cabin absolute pressure to flight absolute pressure will, of course, increase ifja comfortable pressure schedule is maintained for the cabin. AThis ratio of pressures actually very closely approximates the ratio of outlet pressure to inlet pressure of the air delivery means as ambient air at ambient pressure is drawn into the air delivery means and forced into the cabin under a pressure higher than cabin air pressure. Once the ratioof cabin absolute` pressure to flight absolute pressure eX- ceeds the 4compression ratio of the air delivery means, the latter fail to furnish air to the cabin at controllable or known pressures. The resultant pressure A'si-irgings' or pulsations obviously will produce rapid ychanges in the cabin absolute pressure and'v render control of cabin absolutepressure along a desired schedule substantially impossible.A The compression ratio of the air delivery means of any pressurizable cabin aircraft, thereforaimp'oses a limit on the altitude to which the aircraft can be own. e

The instrument of the present invention in the broadest aspects thereof comprises means, operable in accordance with a selected ratio of cabin absolute pressure to ight absolute pressure, adapted to cooperate with the means of the system for varying the rate of air discharge from the cabin relative to the rate of air delivery to the cabin to maintain such ratio substantially constant above an altitude at which cabin absolute pressure would tend to exceed the value sensing the ratio of cabin absolute pressure Ato flight absolute pressure can also be used to effect necessaryto provide the pe-selectedratio. yThe 1 instrument of the present invention thus insures *thaty the superchargers or'blowers will not be forced even at extremely high altitude flight to e l operate againstya compression ratio beyond the f range in which'the s uperchargers or blowers will give .satisfactory service. This makes it possible to maintainjthevsupercharger system in operation throughout the ventire altitude range in which the aircraft Vfis capable'of flight without limitation by characteristics ofthe air supply equipment used.

The instrument of the present inventioncan ,i be used in any control systemffor regulating the absolute pressure withiny the cabin rand will act to hold thesratio ofpabin absolute pressure'rto flight absolutepressureto a preselected value regardless of the pressure schedule of the cabin prior to the time theiratio rof cabin absolute pressure to `iiight absolute vpressure equaled thev preselected ratio. .The'pressure responsive means 4other control actions to -bring about a desired -pressure schedule for the, cabin atA altitudes lower than the altitude at which the desired ratio control is made effective.V v Q g I f Other features and Aadvantages ofA the present inventionk will be hereinafter apparent from thefollowing description, i particularly-joinentaken in connectionwith the accompanying drawing in nwhich:

Figure 1 Vis a viewpartly in section` and partly in elevation ,ofone embodimentof'the nstru.v

ment of the present invention together withfa diagrammatic showing ofone control system with whichrthe' instrument .can be used;

Figure v2 is a View similar to Figure` lujwbut showing a modified form ofthe instrument;

Figure v3 is'a schematicfshowing of another embodiment of the present invention and shovv-` ing the electrical circuits controlled thereby; and

Figure vi is a graphic plot of the pertinent presf sure control relations between cabin pressure and flight altitude for explanation of the present invention.

The embodiment ef the instrumentar the y the case I0 with the interior of the cabin in' which the instrument is mounted. The case I0 houses a suitable frame I2 on which is mounted a hollow spool I3, the frame being insertable through the opening in the case sealed by the wall element II. A differential pressure capsule assembly I4 is rigidly secured to the one end of the spool I3 and the interior of the latter directly communicates with the interior of the capsule assembly. A tube I5 communica-tes the interior of the spool-I3 with the interior. of a hollow fitting I6 fixed to the one wall of the case I0. An opening I1 formed in this wall of the case is adapted to receive the one end of a conduit or tube led to the exterior of the aircraft to the end that the interior of the fitting I6 is exposed to ambient flight pressure. This pressure is thus communicated through the tube I5 to the interior of the diierential pressure assembly I4. As the interior of theV case I0 is subjected to the absolute pressure within the cabin, it will be seen that the capsule assembly I4 will respond to changes `cabin dierential pressure. 3` c i A control arm I8 ispivotally mountedadjacent one end thereof to anishaped support I9 fixed to the frame I2.. `To .counter balance the arm I8, a weight 2I is rthreadedly mounted to the one end of the armf'for'ino'vement longitudinally of the same. The control .arm I8 and the capsule assembly I4 are pivotally interconnected through a short link 22, the opposite ends of which are connected respectively to the movable end of the capsule assembly I4 and the control arm I8 through suitable pivot pins.

-The angular position of control arm I8 is thus -varied by expansion or contraction of the capsule assembly :I4 to move the free end of `the arm I8 ,between a pair of contacts 23 and 2,4. carried by threaded rods 25 and 26 respectively. The rods 25 and 26 are ,threadedly mounted in tapped openings formed in lingers 21 and 2S respectively, suitably supported on the frame ,I2 and insulated therefrom. It will thus be seen that thecontacts 23 Vand 24 can be adjusted relative to each other by rotation of the rods 25 and 26. A bumper 29 formed by an extension A of the finger 28 limits the angular deflection of the control rod I8.

Conductors30, 3| and 32 lead from the contacts .23, 24 and the control arm I8 respectively,

toa suitable leadinreceptacle 33 which takes an` attachment cap, not shown, carrying contacts connected to control circuits of the cabin pres- Vsurization system. To illustrate the operation of .the instrument nowbeing described, there is illustratedin AFigure l a schematic showing of a control circuit with which the instrument -can be used. In this system, a motor 35 through a suitable gear trainl, not shown, operates a valve 36 used to control the rate of air dischargedr from `thecabin. The motor 35 is reversible and may be energized either through the field coil` 31 or 38 by power from some suitable sourcefsuch asthe battery 39, to move the valve in alternate directions, depending upon 'the direction of rotation of the motor 35.

Automatic control of the valve 36 is efected through a control relay 4I which, as shown for illustrative purposes, is` essentially a power amplifier in which very small currents from a battery 42 can be used to selectively energize the coils 43 and 44 of the relay 4l to control a flow of relatively large-currents in the circuits of the motor iield coils 31 and 38. Energization of relay coil 43 causes the armature 45 of the relay to move to the left, as viewed in Figure ,the circuit'of the field coil 38.

l, and into engagement with a contact 46 against the action of one of a pair of centering springs 41 to complete a circuit from the battery 39 through the circuit of the field coil 31. Energization of this eld coil produces such rota.- tion of the motor to drive the valve 36 toward a closing position to decrease the rate of air discharge from the cabin. Energization of relay coil 44 causes the armature 45 of the relay to move to the right, as viewed in Figure 1, to engage with contact 48 against the action of the other of the pair of centering springs 41 to complete a circuit from the battery 39 through The completion of this circuit, as should now be understood, causes the motor to drive the valve 35 in the opposite direction, that is, towards an open position to increase the rate of air discharge from the cabin.

Energization of the relay 4I is in part controlled by pressure responsive means schematically shown atr49. The control means schematically` shown at 49 may comprise any control elements desired which will regulate cabin pressure along some preselected or desired pressure schedule as the aircraft is flown at altitudes at which pressurization is desired.

Figure ll-illustrates in graph form,.inlwhich flight altitude is plotted against pressure, alternate forms of pressure schedules possible with the control means 49. In one schedulerepresented by broken line A, the control means 49 acts to hold the cabin absolute pressure substantially constant after the aircraft has reached an altitude of 8000 feet, cabin absolutepressure remaining constant until the aircraft has ascendedv to an altitude, in the illustration now being explained, of approximately 21,000 feet. At this altitude thevdiiferential between cabin absolute pressure and night absolute pressure will have equalled the predetermined differential pressure set by the bursting strength of the cabin. In the schedule represented by broken line B 'control means 49 has progressively decreased cabin absolute pressure as the aircraft ascended beyond 5000 feet altitude until the differential pressure limit was reached.

As the control means 49 is electrically connected vby leads 5I and 52 to the relay coils 43 and 44 respectively, it will act through suitable switch means to energize one or thev other of the coils depending upon the pressure values affecting the control means 49. The control means 49 is also connected by a lead 53 to the conductor 3| of the instrument now being described, which as previously explained is connected to the contact 24. This lead 53 in effect forms a grounding connection for the control means 49, for the latter is grounded only when the control arm I8 of the instrument is in engagement with the contact 24. It will thus be seen that if the control arm I8 has moved out of engagement with the contact 24, the control means 49 is prevented from effecting any control action on the relay 4 I The conductor 30 of the instrument connected to the contact 23 is electrically connected to the coil 44 of the relay 4I by a lead 54 so that movement of the arm into engagement with this contact reswl'is in ener intion of the coil 44. Energiration of the coil 44, it will be remembered, results in opening movement of the valve 36.

Control arm I8 is held in engagement with ground circuit 24 as long as the pressure differential acting on the differential pressure capsule assembly I4 is less than the predetermined value fixed by the structural strength of the cabin. Whether the control means 49 is regulating cabin absolute pressure along schedules represented byl opening movement of the control valve 36. The

instrument will thereafter elect a control schedule represented by line C of the graph of Figure 4.

The instrument of Figure 1 is arranged furthermore to decrease the limit differential Pressure in accordance with a xed limiting ratio of the absolute pressures existing across the pressure capsule assembly I4. This ratio is a preselected one and is substantially that of the compression ratio of the superchargers or blowers used to furnish air under pressure to the cabin. This limiting ratio function is derived from the action of an evacuated capsule or aneroid 56 on the differential pressure capsule I4. The aneroid capsule 56 is supported by a ring 51 carried byA a slide 58 mounted on an enlarged portion 59 of the frame `I2. An adjusting screw 6I carried by an upstanding boss 62 formed integral with theenlarged portion 59 of the frame uI2 permits the slide 58 and the aneroid 56 to be adjusted longitudinally of the frame I2. A second adjustment screw`63 permits axial adjustment of the fixed side of the aneroid 56 with respect to the slide 58.

A post 64 carried by the expandable side of the aneroid 56 is adapted to engage against the underside of the control arm I8 to augment the action of the diiferential pressure capsule I4 on the control arm wheneveraneroid 56 expands more than a predetermined extent as aresult of I the reduction of cabin absolute pressure below a predetermined value. By adjustment of screws 6I and 83 the position of the aneroid can be selected which will bring about the desired cooperation between the same and thefdifferential pressure capsule assembly I4 to maintain a balance of the control arm I8 between the contacts 23 and 24 in accordance with a preselected ratio of cabin absolute pressure to flight absolute pressure whenever control means 49 seeks to control operation of the valve 36 which would result in a cabin compression ratio in excess of the preselected value. This control of cabin absolute pressure is represented by the line D in the graph of Figure 4.

It will be seen that as long as pression ratio remains the pre-selected one, control arm I8 will be disposed between contacts 23 and 24, but should the preselected compression ratio be exceeded, action of the capsules I4 and 58 will move the control arm I8 against contact 23 resulting in energization of motor field coil circuit 38 and opening movement of the valve 3S to reduce the absolute pressure within the cabin and consequently the cabin compression ratio.

There is shown in Figure 2 an instrument'in which pressure control members forming a, part of the control means 49 inthe schematic system shown in connection with the instrument of Figure l, are actually a part of the instrument. This avoids the necessity of using separate control instruments in the Valve control system. The control instrument as shown in Figure `2 comprises a sealed case 1I of insulating material, the one wall of which is formed withf'a the cabin com- '6 tapped opening 12 for receiving one end of Ya tube or conduit, not shown, communicating with the interior of the cabin. The case 1I houses a suitable frame 13 to which ismounted a capsule assembly 14. A tapped opening 15 formed in the one wall of the case 1I is adapted torre'- ceive one end of a suitable tube or conduit, not shown, but leading to the exterior of the-cabin, that is, to flight ambient pressure. A small con'- duit 16 leads from the tapped opening 15 tothe v interior of the capsule assembly 14. As the interior of the case 1I is subjected tocabinpressure and as the interior of the capsule assembly 14 issubjected to ight or ambient pressure, it will be seen that the capsule assembly 14 is a differential pressure capsule and will respond to changes in the cabin differential pressure.

A short link 11 pivotally interconnects themovable side of the capsule assembly 14 and a control arm 18 pivotally mounted at 69 to a iinger 10 depending from the frame 13. The opposite end of the control arm 18 is movable between contacts 19 and 8I carried by threaded studs 82 and 83 respectively, adjustably carried by -ngers 84 and 85 supported on the frame 13 and insulated therefrom.

Mounted to a Wall element closing the end of the case 1I at the end opposite to the-differential pressure capsule assembly 14 is Ian evacuated capsule or aneroid 8B. The one end of this capsule or aneroid is fixed relative tothe-frame 13 and the opposite or movable end ispivotally interconnected by means of a short link-81 toa second control arm 88 pivotally mounted at 89 to a linger 9| depending integrally from the-frame 13V. The opposite end of this control arm moves between contacts 92 and 93 carried by threaded stud-s 94 and 95 respectively, adjustably'carried by bosses 96 and 91 supported on the frame 13 and insulated therefrom.` Control arm 88 is electrically connected by a lead 98 to contact 19 engaged bycontrol arm 18 only so long as `thelcalapin differential pressure is below some preselected Value determined by the bursting strength'of the cabin structure. Control larm 18 is grounded as indicated at 99 so `that the aneroid-88 isoperable 4to control cabin absolute pressure as long as contact arm 18 is engaged with the contact 19.

Theform of the motor control'circ'uit shown with .instrument of Figure 2 is identical tothe control circuit -shownin Figure l. It will thus be `seenltliat with control arm 18 engaged with the contact 19, movement of control arm ibetwee'n and into engagement with contacts92 and 193 will result Vin suchenergization of the relyM as to close and open the control valve 38re'spectively. vThisis so, for when contact arm 88"is`engag`ed with contact 92 relay coil 44 is energized to result in movement of the armature 45 into engagement withtheA contact 48 to close a circuit through-the motor field coil 38, which, as previously explained,

results in Isuch rotational movementof the motor 35 as to drive the valve toward open position?" On the .other hand, when the aneroid expands4v because of lessening cabin absolute pressure andthe .arm 88 is moved to the right and intovenga'geme'nt has been flown to some preselected altitude, to maintain cabin absolute pressure at a constant value even though the aircraft ascends to altitudes above the apparent altitude of the cabin. Such a cabin pressure schedule is represented by the line A of Figure 4. When the aircraft reaches that altitude at which cabin diftedential pressure is equal to the preselected differential pressure,

the arm 18 will move out of engagement with the contact 19. Disengagement of the arm 18 from the contact 19 disrupts or breaks the grounding circuit established by the lead 98, control arm 18 and ground 99, to render the aneroid inoperative to thereafter control cabin absolute pressure. If the aircraft continues to ascend, the arm 18 will be swung into engagement with the contact 8| as the differential pressure capsule assembly 14 further contracts. Engagement of the control arm 18 with the contact 8| results in energization of the coil 44 of the relay 4| which as previously explained results in movement of the armature 45 into engagement with the contact 48, thereby energizing motor eld coil 38 to bring about opening movement of the valve 36.

The differential capsule 14 will thereaftercontrol or regulate pressure within the cabin to maintain a constant differential pressure, represented by line C in Figure 4, until such time as the ratio -of cabin absolute pressure to ight absolute pressure equals or exceeds the compression ratio of C the action of the diierential pressure capsule 14 on the control arm 18.

`To permit this control action by the aneroid 86, the control arm 88 must be formed of such a material that the arm will flex or yield under` the force developed by the expanding aneroid 86. This is so, for at the time the aneroid commences its coaction with the differential pressure capsule, the free end Vof the control arm 88 will be in engagement with the contact S3. Thus the medial vportion of the arm 68 must flex to the right to urge the projection I Il into pressural engagement with the projection 62 carried by the control arm 18.r The coaction of the aneroid and diiferential capsule assemblies will hold the ratio of cabin absolute pressure and flight absolute pressure substantially constant and this pressure schedule is shown yby line D of Figure 4.

The interconnection between the aneroid 86 andthe control arm 18 embraces a regulation responsive to external tempera-ture variations. This regulation is shown as an expansible iiuid filled bellows |03, this bellows being connected by a flexible tube |04 to a port |05 adapted to receive a tube or conduit leading to ambient temperature. Accordingly, as the temperature of the external or ambient air varies, the bellows |03 will expand or contract to bring about the coaction between the aneroid 86 and the control arm 18 at varying altitudes depending upon the ambient air temperature.

`In all of the instruments embodying thev present invention heretofore described, the control action of the instrument is brought about by a contact arm moving into and out of engagement Vwith contact elements. The present invention is not intended to be limited to such an instrument for actually the present invention in the broadest aspects thereof encompasses all means for effecting a control action through the coaction of pressure lresponsive capsule assemblies operatively connected to a movable element which is moved by the capsule assemblies in accordance with a selected ratio of cabin absolute pressure to flight absolute pressure.

There is shown in Figure 3 an instrument schematically indicated at |45 which includes a control arm |46 pivotally mounted as indicated at |41.. The control arm |46 is operatively connected to a plurality of pressure sensitive capsule assemblies, not shown, but which will move the control arm |46 in opposite directions indicated by the arrows |44 and |48 depending upon the relationship of cabin absolute pressure to flight absolute pressure.

The control arm |46 carries at its outer or free end a core element |49 arranged transversely of the arm |46. The opposite end portions of the core element 49 are coaxially disposed within spaced coils |5| and |52 series connected into a circuit |53 which includes a source -ofalternating current |54 and a manually oper- -and|52"are`coils |56 and |51 respectively. so

formed that the end portions of the core element |49 traverses the turns thereof as the arm |56 is pivotally moved under the urgings of the pressure change responsive capsule assemblies connccted to the arm |46. The coil |56 is series connected with a coil |58 while coil |51 is connccted with a similar coil |59. The coils |56 and |59 circumscribe theopposite ends of a core element |6| mounted for longitudinal movement but yieldably held'by contact of arm |60A with centering springs |62; similar to spring 41 of the previously describedV control'circuit, in a center or neutral position. The normal position ofthe core element|6| is shown in Figure 3 and in this position theopposite end faces thereof are spaced from xed contacts |63 and |64 connected respectively to `motor field coil circuits 31 and 38.

-In the operation 'of the instrument now being described, if the arm |46 is moved in the direction of the arrow |44, the one end portion of the core element |49 progressively traverses the turns of ythe coil |56 to induce in that coil and consequently coil |58, an electro-magnetic ilux sucient to draw or attract the core |6| upwardly and into engagement with contact |63. As'the core |6| is grounded, as indicated at |65, movement of the end face of the core into engagement with the contact |63 will complete a circuit through the motor field coil 31 which, as previously explained, results in a closing movement of the valve 36.

On the other hand, if the core element |49 moves'between the turns of the coil |51, the current induced in that coil and consequently the coil |59, will draw the armature |6| downwardly, as viewed in Figure 3, and into engagement with contact |54. It should now be obvious that engagement of the core |6| with the contact |64 energizes the motor eld coil 38 to produce opening movement of the valve 36.

It will now be seen that each illustrated embodiment of the present invention is one which is operable in accordance with a selected ratio of cabin absolute pressure to flight absolute pressure-and adapted to cooperate with the valve erases operating means of a pressure control system to so operate said valve as to maintain such ratio substantially constant at all altitudes above some datum altitude. It will be seen that the control arm of each embodiment of the invention herein illustrated forms actuator means which, in cooperation with the contacts or coils of the instrument, form selecting means for bringing about the necessary change in cabin absolute pressure to maintain the desired ratio of pressures `substantially constant. The control arm or lever together with the contacts or coils thus form control effecting means adapted to be operatively connected to the valve operating means of a system such as illustrated in the drawing.

Although all embodiments of the present invention have been herein shown and described as instruments controlling electrical systems, it should be obvious 'that other types of motivating systems could be used such as hydraulic or pneumatic, as the particular typeof system is not important to the invention herein disclosed.

Although the now preferred embodiments of the present invention have been illustrated and disclosed herein. it is to be understood that the invention is not to be vlimited thereto for the same is susceptible to changes in form and detail withinthe scope of the appended claims.

I claim:

l. An instrument for use in a system for regulating pressure in an aircraft cabin which system includes meansV to effect and control air outflow from the cabin, comprising: a housing to be mounted within said cabin and including means for communicating the interior of said housing with the interior of said cabin; a first capsule mounted Within said housing; means ca rried by said housing adapted to be connected to flight absolute pressure and communicating with the interiorof said first capsule whereby the latter is to be subject to, and movable in response to changes in, the dierence between cabin absolute pressure and flight absolute pressure; control effecting means including means adapted to be operatively` connected to the means of saidv system for effecting and controlling outflow of air from the cabin; means operatively connecting said first capsule to said control effecting means whereby the latter is motivated by pressure change responsive movements of said capsule; an evacuated capsule mounted within said housing, exteriorly subject to cabin absolute pressure, and movable in response to changes in cabin absolute pressure; said capsules being so mounted within sai-d housing as to be in mechanical force transmitting relationship with each other and so arranged that expansionvof saidV evacuated capsule forcibly opposes expansion of said first capsule as said evacuated capsule expands in lresponse to vdecreasing cabin absolute pressure during ascent of said aircraft; said evacuated capsule acting, Whenever the ratio of cabin absolute pressure to flight absolute pressure exceeds a preselected value'l to progressively restrain the expansion of said first capsule to produce such motivation of said control effecting means Vthat the latter is adapted to control operation of said outfiow effecting and controlling means of said system to vary cabin absolute pressure in accordance with said preselected ratio of cabin absolute pressure to flight absolute pressure.

2. An instrument for controllably regulating pressure within an aircraft cabin. whereinto air and having means for varying the rate-of air discharged therefrom, comprising: a pivotally mounted lever; a pressure responsive device adapted to be subjected to, andA movable in response to changes in, the difference between cabin absolute pressure and flight absolute pressure; means interconnecting said lever and said device whereby said lever-,is moved by said device as it moves in response to changes in the difference betweenv said pressures; a second pressure responsive device adaptedto be mounted within the cabin and subjected to, and movable in response `to changes in, cabin absolute pressure; and means carried by said second pressure responsive device cooperatively associated with the lever and arranged solidly to engage said lever to forcibly resist movement of said lever because of expansion of said first device as said second device expands in response -to decreasing cabin absolute pressure during operation of the aircraft within an altitude range in which the ratio of cabin absolute pressure to flight absolute pressure exceeds a predetermined value.

3. An instrument for use in a system for regulating pressure in an aircraft cabin which system includes means to effect and control airy outflow from the cabin, comprising: a housing to be mounted within said cabin and including means for communicating the interior of said housing with the interior of said cabin; a first capsule mounted within said housing; means carried by said housing adapted to be connected to flight absolute pressure and communicating with the interior of said first capsule` whereby the latter is tofbe subject;to, 4and ymovable in response to changes in, the-difference between housing pressure and flight absolute pressure; a second capsule mounted within Vsaid housing, exteriorly subjected to housing pressure, and movable in response to changes in housing pressure; said capsules being so arranged that expansion of said second capsule will-,forcibly oppose expansion of said first capsule to modify the pressure change .responsive movements of saidrst capsule to produce a resultant movement as said capsules conjointly move in response to changes in housing and flight absolute pressures; a control effecting means including means adapted to be operativelyfconnected to the means of the system effecting and controlling outiiow of air from the cabin; and means motivating said control ef.

fecting means through the resultant movement of said capsules as the same conjointly move in reto be subject to, and movable in responseto.

changes in, the difference between cabin absolute pressure and flight absolute pressure; controlieffecting means; means mcvably mounting said control eiectingmeans withinssaid housing; vsaid control effectingY means including means adapted to be operatively connected to the meansof Ysaid systemfor effecting and controlling outflow ofair from Vthe cabin; ,means operatively connecting said first capsule to said control effecting means whereby the latter is moved by pressure change responsive movement of said capsule; an evacuated capsule mounted within said housing; exteriorly subjected to cabin absolute pressure, and movable in response to changes in cabin absolute pressure; said capsules being so mounted within said housing as to be in mechanical force transmitting relationship with each other and so arranged that expansion of said evacuated capsule forcibly opposes expansion of said first capsule as said evacuated capsule expands in response to decreasing cabin absolute pressure during ascent of said aircraft; said evacuated capsule acting, whenever the ratio of cabin absolute pressure to iiight absolute pressure exceeds a preselected value, to progressively restrain the expansion of said first capsule to produce such movement of said control effecting means that the latter is adapted to control operation of said outflow effecting and controlling means of said system to vary cabin absolute pressure in accordance with said preselected ratio of cabin absolute pressure to flight absolute pressure.

5. An instrument for controllably regulating pressure within an aircraft cabin whereinto air is continuously supplied by an air delivery means and having means for varying the rate of air discharge therefrom, comprising: two pressure sensitive means, the first of said pressure sensitive means adapted to be responsive to changes in cabin absolute pressure; and the second being adapted to be responsive to the difference betweencabin absolute pressure and flight absolute pressure; control effecting means adapted to be operatively connected to said varying means, said means including means moved by said second pressure sensitive means in response to changes in the difference between cabin absolute pressure and flight absolute pressure to regulate said varying means to effect a control of cabin absolute pressure to maintain the difference between said pressures substantially constant; and means carried by said first pressure sensitive means and movable thereby into engagement with said movable means at a preselected cabin absolutev pressure to resist increase ofy cabin absolute pressure movement of said movable means whenever said second pressure sensitive means thereafter responds to a decrease in the difference between cabin absolute pressure and flight absolute pressure to maintain cabin absolute pressure in accordance with a predetermined ratio of cabin absolute pressure to flight absolute pressure.

6. An instrument for use in a system for regulating pressure in an aircraft cabin which system includes means to effect and control air outflow from the cabin, comprising: a housing to be mounted within said cabin and including means for communicating the interior of said housing with the interior of said cabin; a first capsule mounted Within said housing; means carried by said housing adapted to be connected to'fiight absolute pressure and communicating with the in-` terior of said firstcapsule whereby the latter is to be subject to, and movable in response to changes in the difference between cabin absolute pressure and iiight absolute pressure; control effecting means adapted to be connected to the airflow control means of said system, said control effecting means being operatively connected to said first capsule and motivatedl by pressure change responsive movements of saidI capsule to produce operation of said outflow controlling means in a manner which will maintain cabin differential pressure at a preselected constant value throughout a medium altitude range; a second capsule mounted within said housing subject to, and movable in response to changes in cabin absolute pressure; said first and second capsules being so arranged that a preselected expansion of said second capsule will forcibly oppose expansion of said first capsule; means carried by said second capsule and movable therewith as said second capsule expands in response to decreasing cabin absolute pressure as said aircraft ascends beyond said medium altitude range; said last named means, upon attainment by the aircraft of an altitude where the ratio of cabin absolute pressure to ight absolute pressure equals a preselected value, being operative to establish mechanical force-transmitting relationship between said capsules, and co-acting with said second capsule to so modify the pressure change responsive movements of said first capsule as said aircraft ascends beyond said altitude as to thereafter, throughout a higher altitude range, produce such motivation of said control effecting means that the latter is adapted to control operation of said outflow controlling means to vary cabin absolute pressurein accordance with said preselected ratio of cabin absolute pressure to iiight absolute pressure.

'7. An instrument for use in a system for regulating pressure in an aircraft cabin which system includes means to effect and control air outflow from the cabin, comprising: a housing to be mounted within said cabin and including means for communicating the interior of said housing with the interior of said cabin; a first capsule mounted within said housing subject to, and movable in response to changes in cabin absolute pressure; a second capsule mounted within said housing; means carried by said housing adapted to be connected to flight absolutepressure and communicating with the interior of said second capsule whereby the latter is to be subject to, and movable in response to changes in, cabin differential pressure; control effecting means including means adapted to be connected to the airflow control means of said system, said control effecting means being operatively connected to said first capsule and motivated Iby pressure change responsive movements of said capsule to produce operation of said outow controlling means in a manner which will maintain cabin absolute pressure at a preselected constant value throughout a medium altitude range; means operatively connecting said control effecting means to said second capsule to produceoperation of said control effecting means, whenever the difference between cabin absolute pressure and flight absolute pressure reaches a preselected difference, in a manner which will maintain the difference in said pressures substantially constant and equal to said preselected difference as said cabin absolute pressure decreases during ascent of said aircraft higher than said medium altitude; said first and second capsules being so arranged that a, preselected expansion of said first capsule will forcibly oppose expansion of said second capsule; means carried by said ,first capsule and movable therewith as said first 'capsule expands in response to decreasing cabin absolute pressure as said aircraft ascends beyond said medium altitude range; said last named means, upon attainment by the aircraft of an altitude where the ratio of cabin absolute pressure to flight absolute pressure equals a preselected value, being operative to establish measia-,82s.

chanical force-transmitting relationship between said capsules, and co-acting with said rst'capsule to sovmodify the pressure change responsive movements of said second capsule as said aircraftascends :beyond said altitudeasv to thereafter, throughout a' higher altitudeV range, produce vsuch motivation of said control Aeffecting 'means-that the latter is adapted to control operation ofsaid outflow controlling means to vary cabinabsolute pressure in accordance with said preselected ratio of cabin absolute pressure lto ight absolute pressure. f A

8. An-instrument for use in asystem for regu--` lating pressure in an aircraft cabin-which system` includes means to effect and control air outflow from the cabin, comprising: a first capsule to b'e: mounted Within said cabin and including 'means adapted to be connected to flight absolute pressure and communicating with the interior-of 'said-v rst capsule whereby the latter is'to` be subject to, and movable in response to changes in, lthe difference between cabin absolute pressure and flight absolute pressure; a pair ofcontacts' including means adapted to beA operativelycon-v nected to the outflow effecting and'l "controllingmeans of said system; 'a control-arm having-one end thereof disposed between=saidcontacts for movement into engagement with'cne`or:theotherof said contacts, depending upon the direction of movementv of said arm, to thereby control operation of said outow controllingmeans; meansoperatively connecting said flrst capsule to saidy control arm whereby pressurechange responsive movement of said first capsule actuates said arm to move the one end thereof into engagement with one or the other of said contacts; a second capsule to be mounted within said cabin and to be subject to cabin absolute pressure and movable in response to changes therein;` said capsules being so mounted within said housingas to be4 in mechanical force transmitting relationship- With each other and so arrangedthat expansion of said second capsule will forcibly-'oppose-expansion of said first capsule, said second capsuleacting, whenever the ratio of cabin absolute pres-` sure to flight absolute pressure exceeds a'A preselected value to resist movement of said control arm resulting from expansion of said-rst'capsule in response to a decrease in the diierence between cabin absolute pressure and flightabsolute pressure to produce suchv actuation of' said con-v trol arm that the latter is adapted tocontrol operation of said outflow control means to vary cabin absolute pressure in accordance with said preselected ratio of cabin absolute-pressure--to flight absolute pressure. f

9. An instrument for use in a system for regulating pressure in an aircraft cabin which -sysi tern includes means to eiect `and control air outflow from the cabin, comprising: a housing to be mounted within said cabin and including means for communicating the interior of said housing with the interior of said cabin;'a

first capsule mounted within said housing;

means carried by said housing adapted to be connected to ight absolute pressure andcommunicating with the interior of said first 'capsule whereby'the latter is to be subject to, and movable in response to changes in, the difference between cabin absolute pressure and fiight .ab"

solute pressure; a pair of contacts including means adapted to be operatively connected to the outow eiectingvand*controlling means-of said system; means formounting said contacts` withinA said housing for relative movement therebetween Vwhereby thespacing cf saidcon-y tacts may be selectively varied;a control arm;4 means for pivotally mounting said controlarm within said housing with the fone end vofnsaidarmv disposed between said contacts for movement into engagement with one sor rthe. otherof .said contacts, depending upon the directiony of movement of said arm, t-o ,therebyfcontrol cperation of said outflow controlling means; meansv operatively connecting said rst capsulevto. said control .arm whereby pressure.r changeA responsive,.movement of said first capsuleis adapted togactuate said arm to movev the one end there-V of into engagement with `onefl-,or the,Y other of.

said contacts; a second capsule mounted .within'saidhousing to be subject to cabin absolute pressure` and-movable in` response to changes' inricabin absolute pressure, said capsules being so vmounted -within said housing as to be in me-` chanical force transmitting relationship -with each-'other and-so arranged that expansionof said: isecond capsule-will forcibly oppose expansionilof said irst` capsule, said second; capsule acting, l whenever the ratio of cabin absolute pressure to flight absolute pressure exceeds a preselected value to resist movement of said control arm-:resulting from expansion of said first capsulein response to a Adecrease-.in the difference be-4 tweenv cabin absolute pressure an'd flight absolutev pressure to produce such actuation of said kcontrol arm that the latter is adapted to control operation of said outflow control means to vary cabin. absolute pressure in accordance with said preselected ratio of cabin absoluteL pressure to night absolute pressure.

l10;-.An instrument for use in a system ,forregulating pressure in an aircraft cabinv which` system includes means to effect and control air outflow from the cabin, comprising: a housing to beV mounted within said cabin and including means zfor communicating the interior of said housing with the interior of said cabin; a frame element removably mounted within said housing; arst capsule mounted on said element;-

meanscarried by said housing adaptedto be connected to flight absolute pressure and com-A municating with said'- flrst capsule, whereby thelatter is to be subject to, and movable in response to changes in, the difference between cabin absolute pressure and night absolute pressure; `a pair of contacts including means adapted to be yoperatively connected to the outiiow electing and controlling means ofA said system; means for mounting said contacts on saidfelement; a control arm pivotally mounted` on Asaid element with the one end thereof disposedbctween said contacts for movement intoengagement with one or the other of said contacts', depending upon the direction of movementfof said arm, to thereby control operation of said outflow controlling means; means operatively/connecting said first capsule to said control arm whereby pressure change responsive movement of said first capsule actuates saidarmV to move the one end thereof into engagement with one or the other of said contactsl to maintain the difference between cabiny absolute and iiight absolute pressure substantially constant; a second capsule mounted o n saidelement to be subject to cabin absolute pressure and -movable in response to changes therein, said capsules being so `mounted within said housing` as to bein mechanical force transmitting relationship 'with eachother and so arranged that expansion of said second capsule will forcibly oppose expansion ofV said nrst. capsule, said second capsule acting, whenever the .ratio of cabin absolute pressure to flight absolute pressure exceeds a vpreselected value, toI resist movement of said control arm result'- ingf'from expansion of said first capsule `in response to a decrease in the difference between cabin absolute pressure and flight absolute. pressure to produce such actuation of said control armthat the latter is adapted to. control. operation of said outflow controlling means tov vary cabin absolute pressure in accordance with said-preselected ratio'of cabin absolute pres. sureto.` flight absolute pressure.

lil.: An instrument for use in a system for regu.- lating .the absolute pressure in an aircraftcabin. whichsystem includes means to effect andpcontrolv air-.outflow from thev cabin, comprising: a rst. capsule tobe mounted within. said cabin wherebyy the latter is subject to, andmovableiin response to changes in, cabin absolute pressure; a second capsule to be mounted; within. said cabin; means. including'means adapted to be connectedtolflight. absolute pressure, communicating with, the interior; ofy said second capsule whereby thelatter is toA be subject to, and movable in response to. changes in, the difference between cabin absolute. pressure and flight absolute pressure as said aircltasflcascends beyond a selected altitude; means for mounting said capsules in an axially aligned relationship so that expansion of sad'rstzcapsule inl response to a preselected decrease in. cabin absolute pressure will forcibly oppose expansion ofk said second capsule resulting from a decrease in the difference between cabin. absolute pressure and flightI absolute pressure to modify the pressure c hange responsive movements of said second capsule to produce a resultant movement as said capsules conjointly move in response to changes. in cabin absolutev and flight absolute pressures; and control effecting means motivated as a result of an d in accordance with the resultantY movement-of said capsules asthe same conjointlymove in, response to changes in cabin absolute, and. flight absolute pressures, said control; effecting. means including means adapted to be operatively connected with the outflow effecting, and controlling means of saidl system whereby thelatter isadapted to be operated in accordance withv thev motivation of said controleffectingmeans;

l2. An instrument for use in a system for regu.- lating theabsoiute pressure in an aircraft. cabinA which system includes means to effect .andcontrol air outilowfrom the cabin, comprising.: 'a'.rsti capsule to be mounted within said cabin whereby*v the latter is subject to, and movable inlresponse to changes` in, cabin absolute pressureyaxsecond capsule to be mounted'within said cabin;` means; including means adapted to be connected'to flight absolute pressure, and communicating with"v the; interior of said second capsule whereby the latter. is to be subject to, and movable in response toe changes in, the difference between cabin/absolute pressure and flight absolute pressure; control eff'- fecting means, including means adapted to v beoperatively connectedto the means'of said-,systeml for eecting and controlling outflow ofY air. fromi the cabin,` for controlling operation of saidout'- flow effecting and controlling means; said cap.- sules being so arranged-relativeto each otherthatf, expansion of said first capsule-will.forciblyoppose1 expansion of saidsecond capsuleto modifythepressure change responsive movements of s aidg second capsule to produce a resultant movement; asV said capsules conjointly move-in responsewto` changes: in cabin absolute and flight absolute pressures.; and meansl motivating said control effecting means in accordance with the resultant movement of said capsules as the same conjointly move in response to changes in cabin absolute and flight-absolutev pressures, whereby said control effecting means is adapted to control operation of. said4 outflow effecting and controlling means to vary'cabin absolute pressure in accordance with a preselected ratio. of cabin absolute pressure to flight absolute pressure.

13. An instrument for use in a system for regulating pressure in an aircraft cabin which system includes meansv to effect and control air outflow from the cabin,` comprising: a housing to be mounted within said cabin and including means forI communicatingr the interior of said housing withy the interior of said cabin; a first capsule; means for mounting. saidiirst capsule within said housing; means carried by said housing adapted to be: connected to night absolute pressure and communicating with sai-d rst capsule whereby the latter isV to be subject to and movable in response to changes in the difference between cabin. absoluteV pressure and flight absolute pressure; a second capsule; meansfor mounting said second capsule within said housing whereby said capsule is to be subjected to,l and movable in response to changes in, cabin absolute pressure; a control effecting means including means adapted' to be operatively connected to the means of the system effecting; andcontrolling outflow of air from the cabin; said capsules being so mounted withinsaidv housing asto be in anaxially aligned relationship. andeach movable, during changes in the pressures tor which they are subject, in coincident linear paths of movement and so arranged that expansion of said second. capsule forcibly opposes expansionr of said iirst'capsule as said second capsule expands in response to decreasing cabin absolutepressure during'l ascent of said aircraft; and meansl carried by said second capsule and, upon.l the attainment by said aircraft of an altitudev-at which the ratio of cabin absolute pressure toflightabsolute pressure is substantially equal to-a` preselected value;coacting with said' control eflecting'means to'progressively resist movement of' said first capsule ink response to a decrease in: the difference betweencabin absolute pressure and :flight-absolute pressure to produce such moti- 'vationA of said control effecting means that the latter is adaptedto-control operation of saidoutflow effecting' and controlling means of said system-tovary cabin absolutepressure in accordance with said preselectedA ratiolof cabin absolute presf sure to flight absolute pressure.

lfl A-n instrument for use in a system. for regulatingpressure; in anl aircraft cabin which system includes meansto effect; andcontrol' air outflow. from.the cabin, comprising: a housing to be v mounted withinsaidcabinl and including means f absolute pressureandI communicating with said.

first capsule whereby the latter is' to be subject to and. movable inresponse toA changes in, the difference, between cabin. absolute pressure and flight absolute pressure; asecondcapsule mounte'd within said' housing toV be subjected to, and.

movable in response to changes in. cabin absolute-pressure: acontrolieiecting means including means: adapted-tobeoperatively connected to the means-of the systemveffecting andc'ontrolling out- 1low:of; air from. the cabin;A meansY operatively connecting the first capsu'lejtofsaid control effect'- ing means 'whereby the latter is motivated by pressure change responsive movements vof, said first capsule, .independently of vsaid second capsule so long as theratio ofcabin absolute pressubstantially equalV to a v'preselected value, operaNV tively connected with saidfcontrol elfecting means to establish mechanical force-transmitting relationshp between said capsules and coacting with said second capsule to progressively resist the moving force of said first capsuleinv response to a decrease in the diiference between cabin absolute pressure and flight absolute pressure to produce such motivatonfof said `control eifecting means that the latter is adapted to control operation of lsaid outflow effecting and controlling means or said system to vary cabin absolute pressure in accordance with said .preselected ratio of cabin absolute pressure 4to Vflight absolute pressure. f Y f l5. An instrument forl usel in a system for regulating pressure in an aircraft cabin whichcsystem includes means to effect and control air outflow from the cabin, comprising: control eifecting means, including means adapted to be operatively connected to the means of the system effecting and controlling air outflow from` the cabin; a rst capsule to be subjected to, and movable in response to changes in, cabin absolute pressure; means operatively interconnecting said first capsule and said control effecting means whereby the latter is motivated by pressure change responsive movements of said capsule to control operation of said outllow effecting and controlling means to vary cabin absolute pressure; a second capsule to be subjected to,v and movable in respense to changes in, the difference between cabin absolute pressure and flight absolute pressure; means operatively interconnecting said second capsule and said control effecting means whereby said second capsule is operable, upon the attainment of a preselected difference of cabin absolute pressure over flight absolute pressure, to override the action of said iirst capsule on said control effecting means to thereafter actuate said control effecting means to control operation of said outflow effecting and controlling means to so vary the rate of discharge of air from the cabin to maintain the difference between cabin absolute pressure and flight absolute pressure equal to said preselected difference, said capsules Abeing so mounted within said housing as to be in mechanical force transmitting relationship with each other and so arranged that expansion of said rst capsule forcibly opposes expansion of said second capsule as said first capsule expands in response to decreasing cabin absolute pressure during ascent of said aircraft; and means operatively 'assocated with said first capsule and operable at a preselected cabin absolute pressure to coact with said second capsule to so motivate said control effecting means as to adapt the latter to control operation of said outflow effecting and controlling means to decrease cabin `differential pressure at such a rate as flight absolute pressure decreases to maintain cabin absolute pressure rin accord- 118-. ancefwtlia preselected =ratio :of `"cabin labsolute pressure to flight absolute pressure. i

' 16; An instrument for use ina` system for regulatihg' 'pressure in .anv aircraft cabin which system 'includes' means'tojeect and'control air outow from the cabin,` icon uarising:y afhoujsing to be mounted withinsaid cabin and including means forj'communicating' Athel interior vof said vvhousing with theinteri'or of said cabin; a first capsule mounted within said housing adapted tobe subi ject to cabin absolute pressure; a pair ofcontacts including' -rneans' adapted to bev operatively connecte'dft the outflow eiecvtingiand controlling means ofsaidsys'tern;v a control arm pivotally mounted within said housing with thel one end thereof disposed betweenjsaid"contactsfor l movementint'o engagement with onefor the other of said contacts, ldepending lupon the "direction of "movement of-* said arm gto thereby control operation of i'said outilotv controlling j means; means operatively connecting said first capsule to said control arm whereby pressure change responsive-mbvements of said rst 'capsule so actulartes said la'rmthat :the latter,` 'coacting with said contacts, visl adapted to vso" control'loperation ofv i sponse to changes in, the difference j betweenv cabin absolute pressure and flight absolute pressure; a second pair of contacts including means adapted to be operatively connected to the outilow electing and controlling means of said system; a second control arm'pivotally mounted within said housing with one'end thereof clisposed lbetween said second pair of contacts for movement into engagement with one or the other of said contacts; vmeans operatively interconnecting said first control arm and a selected one of said'second pair of contacts andcoacting with said second control arm to maintain said first control arm operative to effect actuation ofsaid outiiow controlling means so long as said second control arm is engaging said preselected contact;

means operatively connecting said second capsule to said second control arm whereby pres- 1 sure change responsive movements of said second capsule so actuate said second control arm that the'latter, coacting-with said second pair-"ofv contacts, isadapted to so control'operation oisaid outflow controlling means as to maintain l the diierence between cabin absolute pressure and ight absolute pressure :at a substantially v constant value throughout va higher altitude cabin absolute pressure and flight absolute pressure reaches said predetermined'value,- thereby 'i to render said first control arm inoperative to effect actuation of said routilow controlling.l

means; said capsules being so mountediwithin said housing as to be in mechanical force transmining relationship with each other and so .ar-y i i ranged that expansion vof said vrrst capsule will forcibly oppose expansion of said second capsulejx said rst capsule acting, whenever :thefratio fof cabin absolute pressure-tonight absolute pressure exceeds a preselected'value, vto resist movement of said second control arm resulting from sulting from edecreasein the difference between housing pressure and night' absolute pressure to modify' the pressure chnge responsive movements of' said' flrst` capsuleto ro'dude a resultant movement as said calpsul'e's conjointly move in response t changes in housing and ight absolute pressures; and control eiecting means motivated as a.y result of and inaccordence with the resultant movement of.' seidcapsules as the same. conjointly move in response to changes in housing pressure and flight absolute pressures, said control effecting means including means adapted to be operatively eonnected with the outflow eiiecting end controlling means of said system whereby the latter is adaptedl to be operated in accordance with the motivation o: said control effecting means.

. BRUCE E. DEL MAR.

.REFERENCES CITED The following vreferences are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,208,554 Price f July. 16, 1940 2,396,116 Noxon sf e Mar. 5, 1946 2,450,076 Bechberger i Sept. 28, 1949 2,463,487 Widg'ery et al. Mar. 1, 1949 o 2,549,672 Del Mar Apr. 1'7, 1951 2,549,673 Del-Mr h4-he Apr. 17, 1951 2,549,690 Klemperer Api'. 17, 1951 

